The present invention relates to an assembly structure of a liquid crystal display comprising a liquid crystal display panel, TCPs and a circuit board.
Conventionally, the assembly structure of a liquid crystal panel and driver ICs in a liquid crystal display has been implemented mainly by TCP (Tape Carrier Package) and COG (Chip On Glass) systems.
In the case of the TCP system, as shown in FIG. 5, a flexible board 6 is equipped with a liquid-crystal driver IC 1, output signal lines 2 for delivering an output of the liquid-crystal driver IC 1 to a liquid crystal panel 7, and input signal lines 3 for inputting an outside signal to the liquid-crystal driver IC 1.
The input signal interconnections 3 of the flexible board 6 are electrically connected to a lead of the circuit board 5 located outside the liquid crystal panel 7, and function to transfer the outside signal to the liquid-crystal driver IC 1 through the lead of the circuit board 5.
Further, in order to obtain a high-reliability liquid crystal display having a high drop margin of opposite electrodes of the liquid crystal panel, a line 4 for opposite-voltage use is formed in the liquid crystal panel 7, the flexible board 6 and the circuit board 5.
Due to this arrangement, the circuit board 5 of the TCP system needs a very large number of input lines to supply signals to the input signal lines 3 of the flexible board 6, so that a multilayer laminate board comprising four to eight conductor layers is employed as the circuit board. The size of the multilayer laminate board needs to be 5 mm to 10 mm wide and 0.6 mm to 1 mm thick.
In the COG system, on the other hand, as shown in FIG. 6, a liquid-crystal driver IC 1, output signal lines 2 for delivering an output of the liquid-crystal driver IC 1 to a liquid crystal panel 7, and input signal lines 3 for inputting an outside signal to the liquid-crystal driver IC 1 are provided on a glass substrate in the periphery of the liquid crystal panel 7. Further, a circuit board 5 is provided outside the liquid crystal panel 7, and an input signal is fed from the circuit board 5 to the input signal lines 3 of each liquid-crystal driver IC 1.
Furthermore, in order to obtain a high-reliability liquid crystal display having a high drop margin of opposite electrodes of the liquid crystal panel, a line 4 for opposite-voltage use is formed in the liquid crystal panel 7 and the circuit board 5.
As another example of the COG system, there is also available a method in which lines for inputting a signal directed to the input signal lines 3 of the liquid-crystal driver IC 1 are formed on peripheral part of the liquid crystal panel 7. However, in this case, the lines in the peripheral part of the liquid crystal panel 7 would be increased in number, causing the size of the peripheral part of the liquid crystal panel 7 to be increased, or the lines in the peripheral part of the liquid crystal panel 7 would be implemented by multilayer interconnection, causing the connection reliability to be degraded.
For the circuit board 5 of the liquid crystal display in the conventional TCP system, there is a need of forming a large number of interconnection lines to supply an input signal directed to the liquid-crystal driver IC 1 of the flexible board 6 as well as a signal to the opposite-voltage use line 4. This would cause the size of the circuit board 5 to be increased or involve the use of multilayer interconnection or other techniques, making it difficult to achieve cost reduction.
Therefore, as shown in FIG. 7, by forming a line 8 for electrically interconnecting the lines of the flexible board 6 adjacent to the peripheral part of the liquid crystal panel 7, and by connecting output lines derived from one liquid-crystal driver IC 1 and input lines of the other adjacent liquid-crystal driver IC 1 to each other, the number of interconnection lines of the circuit board can be reduced.
However, as shown in FIG. 7, since the line 8 for electrically interconnecting the lines of the neighboring flexible boards 6, 6 adjacent to the liquid crystal panel 7 and the opposite-voltage use line 4 cross each other (point A), multilayer interconnection needs to be provided, causing a degradation in connection reliability and an increase in manufacturing cost.
Therefore, an object of the present invention is to provide a liquid crystal display which eliminates the need of multilayer interconnection or the like and which is high in connection reliability and low in price, with an arrangement that the lines for electrically interconnecting the lines of the neighboring flexible boards adjacent to peripheral part of the liquid crystal panel and the lines for opposite voltages do not cross each other.
In order to achieve the above object, there is provided a liquid crystal display including a liquid crystal panel in which liquid crystals are sandwiched between a pair of substrates, of which on one substrate are formed a plurality of thin film transistors corresponding to pixels and a plurality of interconnection lines for driving the thin film transistors while on the other substrate are formed opposite electrodes; a plurality of TCPs connected to the liquid crystal panel and each having a liquid-crystal driver IC provided therein; and a circuit board for feeding signals to the TCPs; wherein:
the circuit board comprises first wirings for feeding a signal which is not electrically connected to the liquid-crystal driver IC; PA1 on one side of each of the TCPs are provided a second wiring connected to the liquid-crystal driver IC and connected to a wiring for driving the thin film transistors of the liquid crystal panel, third wirings which are arranged at both sides of the second wiring and connected to the liquid-crystal drive IC and which serve to electrically connect said TCP to its adjacent TCPs in both sides, and a fourth wiring which is formed between the second wiring and the third wirings and which is not electrically connected to the liquid-crystal driver IC; PA1 on one side of the liquid crystal panel are provided a group of the wirings for driving the thin film transistors collectively led out in units of corresponding one TCP, and a fifth wiring for electrically connecting TCPs adjacent to both sides of the group of the wirings; and wherein
the first wiring of the circuit board and the fourth wiring of the TCP, the second wiring of the TCP and the group of wirings of the liquid crystal panel, and the third wirings of the TCP and the fifth wiring of the liquid crystal panel are connected to each other, respectively.
According to the liquid crystal display of the above construction, the TCP is provided with wirings that are not electrically connected to the liquid-crystal driver IC and that are to be connected to the liquid crystal panel, when electrical connection between a TCP and its adjacent TCPs is implemented by using wirings of the liquid crystal panel, routing can be accomplished without involving the crossing between the wirings that are not electrically connected to the liquid-crystal driver IC and the wirings that serve for the electrical connection between a TCP and its adjacent TCPs.
According to the liquid crystal display in one embodiment of the present invention, since input signals for the liquid-crystal driver ICs are obtained from both the liquid crystal panel side and the circuit board side, input signal lines from the circuit board side to the liquid-crystal driver IC side can be reduced to several power supply lines that should be prevented from voltage drops as much as possible, and ten odd to twenty odd other input signal lines can be wired on the liquid crystal panel side. As a result, the area, number of interconnection layers, thickness and cost of the circuit board can be reduced to a substantial extent as much as 50% or more each.
According to the liquid crystal display in one embodiment of the present invention, since peripheral part of the liquid crystal panel except the connecting portions with the wirings of the TCPS is all covered with an insulating film, the routing of wirings for driving the thin film transistors that could conventionally be routed only inside the seal portion of the facing-side glass of the liquid crystal panel becomes possible to route up to regions outside the seal portion. Thus, line angle and line width of the wirings can be broadened so that the non-difective rate of the wiring formation on the panel can be improved.
According to the liquid crystal display in one embodiment of the present invention, since the circuit board can be set on the rear side of one of substrates of the liquid crystal panel by folding the slit portions of the TCPs, a liquid crystal display having a small picture frame can be fabricated.
According to the liquid crystal display in one embodiment of the present invention, since the insulating film is formed at the slit portions of the TCPs, a liquid crystal display which is improved in strength at the folding portions and which is highly vibration-resistant and highly shock-resistant and free from any electrical defects due to adhesion of electrically conductive foreign matters from outside to the wirings can be obtained.